Learning disability and epilepsy in an epidemiological sample of individuals with tuberous sclerosis complex

Background. Intellectual impairments are a recognized feature of tuberous sclerosis complex (TSC), but the frequency and degree of intellectual impairments has not been systematically studied in large epidemiological samples using standardized measures. As such, the form of the IQ distribution (uni or bi-modal) has not been established and the relationship between IQ and other features (e.g.epilepsy history) is poorly delineated. To address these shortcomings, we assessed the intellectual abilities of a large epidemiological sample of individuals with TSC, drawn from the ‘Wessex’ area of SW England and compared them with the abilities of their unaffected siblings. Method. Standardized tests were used to estimate the abilities of 108 (56 males, 52 females, median age=25, range=4–75) individuals with TSC and 29 unaffected siblings (14 males, 15 females, median age=18, range=6–55). Seizure history was obtained from informants and medical records. Results. Estimated IQ was bi-modally distributed: 55.5%had an IQ in the normal range; 14%had mild to severe impairments; and 30.5%had profound disability (IQ